1. Field of the Invention
The present invention relates to a punching device and, more particularly, to a punching device for punching holes in a bicycle rim.
2. Brief Description of the Prior Art
FIGS. 1 and 2 show a conventional device 60 for punching holes in a bicycle rim 70. The device 60 includes a first cylinder 62 and a second cylinder 64 both of which are disposed on a base 61. A sliding frame 63 slidably extending through the base 61 has a first end plate 631 extending perpendicularly from a first end thereof and a second end plate 632 extending perpendicularly from a second end thereof, wherein the first end plate 631 is connected to a first shaft 621 of the first cylinder 62 and the second end plate 632 has a clamp device 6321 disposed on a top thereof. The second cylinder 64 has a second shaft 642 retractably extending therefrom which has a pin member 646 extending longitudinally therefrom. An extending plate 643 is connected to the second shaft 642 and a block 645 is slidably disposed on the extending plate 643 wherein the pin member 646 freely extends through the block 645. A spring 648 is mounted to a casing 649 of the pin member 646 and urged between the block 645 and the second shaft 642. The block 645 has a ring member 647 disposed to a side facing the clamp device 6321 and a tube 644 is connected to the ring member 647 so that the pin member 646 extends through the tube 644. A plurality of the above mentioned devices 60 are arranged in a circle as shown in FIG. 2 and a bicycle rim 70 is disposed to a position by a robot, for example, to be clamped by the clamp devices 6321. The first cylinder 62 of each device is then actuated to extend each respective first shaft 621 so that each sliding frame 63 is moved to shift the rim 70 toward the respective pin member 646. The second shaft 642 of each of the devices 60 is then extended to depress the respective spring 648 and the tube 644 forms a recess in an inner periphery of the rim 70, and then, the pin member 646 punches a hole through a bottom defining the recess of the rim 70. An inherent shortcoming of the device 60 is that two cylinders 62, 64 have to be actuated respectively and this is time inefficient.
The present invention intends to provide a improved device for punching holes in a bicycle rim to mitigate and/or obviate the above-mentioned problem.